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2. Expert assessment of vulnerability of permafrost carbon to climate change

Author

Schuur, E. A. G., Abbott, B. W., Bowden, W. B., Brovkin, V., Camill, P., Canadell, J. G., Chanton, J. P., Chapin, III, F. S., Christensen, T. R., Ciais, P., Crosby, B. T., Czimczik, C. I., Grosse, G., Harden, J., Hayes, D. J., Hugelius, G., Jastrow, J. D., Jones, J. B., Kleinen, T., Koven, C. D., Krinner, G., Kuhry, P., Lawrence, D. M., McGuire, A. D., Natali, S. M., O’Donnell, J. A., Ping, C. L., Riley, W. J., Rinke, A., Romanovsky, V. E., Sannel, A. B. K., Schädel, C., Schaefer, K., Sky, J., Subin, Z. M., Tarnocai, C., Turetsky, M. R., Waldrop, M. P., Walter Anthony, K. M., Wickland, K. P., Wilson, C. J., and Zimov, S. A.

Published
2013
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5. Lagged Wetland CH4 Flux Response in a Historically Wet Year.

Author

Turner, J., Desai, A. R., Thom, J., and Wickland, K. P.

Subjects
WETLANDS, CARBON emissions, FARM manure in methane production, PLANT canopies, PRECIPITATION (Chemistry), WATER temperature
Abstract

While a stimulating effect of plant primary productivity on soil carbon dioxide (CO2) emissions has been well documented, links between gross primary productivity (GPP) and wetland methane (CH4) emissions are less well investigated. Determination of the influence of primary productivity on wetland CH4 emissions (FCH4) is complicated by confounding influences of water table level and temperature on CH4 production, which also vary seasonally. Here, we evaluate the link between preceding GPP and subsequent FCH4 at two fens in Wisconsin using eddy covariance flux towers, Lost Creek (US-Los) and Allequash Creek (US-ALQ). Both wetlands are mosaics of forested and shrub wetlands, with US-Los being larger in scale and having a more open canopy. Co-located sites with multiyear observations of flux, hydrology, and meteorology provide an opportunity to measure and compare lag effects on FCH4 without interference due to differing climate. Daily average FCH4 from US-Los reached a maximum of 47.7 ηmol CH4 m−2 s−1 during the study period, while US-ALQ was more than double at 117.9 ηmol CH4 m−2 s−1. The lagged influence of GPP on temperature-normalized FCH4 (Tair-FCH4) was weaker and more delayed in a year with anomalously high precipitation than a following drier year at both sites. FCH4 at US-ALQ was lower coincident with higher stream discharge in the wet year (2019), potentially due to soil gas flushing during high precipitation events and lower water temperatures. Better understanding of the lagged influence of GPP on FCH4 due to this study has implications for climate modeling and more accurate carbon budgeting. [ABSTRACT FROM AUTHOR]

Published
2021
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7. Biomass offsets little or none of permafrost carbon release from soils, streams, and wild␣re: an expert assessment

Author

Abbott, B. W., Jones, J. B., Schuur, E. A. G., Chapin, F. S., Bowden, W. B., Bret-Harte, M. S., Epstein, H. E., Flannigan, M. D., Harms, T. K., Hollingsworth, T. N., Mack, M. C., Mcguire, A. D., Natali, S. M., Rocha, A. V., Tank, S. E., Turetsky, M. R., Vonk, J. E., Wickland, K. P., Aiken, G. R., Alexander, H. D., Amon, R. M. W., Benscoter, B. W., Bergeron, Y., Bishop, K., Blarquez, O., Bond-Lamberty, B., Breen, A. L., Buffam, I., Cai, Y. H., Christopher Carcaillet, Carey, S. K., Chen, J. M., Chen, H. Y. H., Christensen, T. R., Cooper, L. W., Cornelissen, J. H. C., Groot, W. J., Deluca, T. H., Dorrepaal, E., Fetcher, N., Finlay, J. C., Forbes, B. C., French, N. H. F., Gauthier, S., Girardin, M. P., Goetz, S. J., Goldammer, J. G., Gough, L., Grogan, P., Guo, L. D., Higuera, P. E., Hinzman, L., Hu, F. S., Hugelius, G., Jafarov, E. E., Jandt, R., Johnstone, J. F., Karlsson, J., Kasischke, E. S., Kattner, G., Kelly, R., Keuper, F., Kling, G. W., Kortelainen, P., Kouki, J., Kuhry, P., Laudon, H., Laurion, I., Macdonald, R. W., Mann, P. J., Martikainen, P. J., Mcclelland, J. W., Molau, U., Oberbauer, S. F., Olefeldt, D., Pare, D., Parisien, M. A., Payette, S., Peng, C. H., Pokrovsky, O. S., Rastetter, E. B., Raymond, P. A., Raynolds, M. K., Rein, G., Reynolds, J. F., Robards, M., Rogers, B. M., Schadel, C., Schaefer, K., Schmidt, I. K., Shvidenko, A., Sky, J., Spencer, R. G. M., Starr, G., Striegl, R. G., Teisserenc, R., Tranvik, L. J., Virtanen, T., Welker, J. M., Zimov, S., Institute of Arctic Biology and Department of Biology & Wildlife, University of Alaska [Fairbanks] (UAF), Ecosystèmes, biodiversité, évolution [Rennes] (ECOBIO), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Ecologie des Hydrosystèmes Naturels et Anthropisés (LEHNA), Centre National de la Recherche Scientifique (CNRS)-Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École Nationale des Travaux Publics de l'État (ENTPE), McMaster University [Hamilton, Ontario], 955713, National Science Foundation, OPP-0806394, Office of Polar Programs, Future Forest (Mistra), SITES (Swedish Science Foundation), TOMCAR-Permafrost #277059, Marie Curie International Reintegration, Institute of Arctic Biology, Université de Rennes (UR)-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École Nationale des Travaux Publics de l'État (ENTPE)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Earth and Climate, Systems Ecology, Amsterdam Global Change Institute, Environmental Sciences, Tarmo Virtanen / Principal Investigator, and Environmental Change Research Unit (ECRU)

Subjects
0106 biological sciences, 010504 meteorology & atmospheric sciences, Biomass, F800, SEQUESTRATION, Permafrost, 01 natural sciences, FIRE, wildfire, Klimatforskning, Arctic, вечная мерзлота, Dissolved organic carbon, ECOSYSTEMS, SDG 13 - Climate Action, boreal, General Environmental Science, Total organic carbon, ARCTIC TUNDRA, CLIMATE-CHANGE, Carbon, Climate change, Miljövetenskap, Permafrost carbon cycle, Earth and Related Environmental Sciences, STORAGE, углеродный баланс, particulate organic carbon, Climate Research, permafrost carbon, Soil science, 010603 evolutionary biology, BOREAL FOREST, биомасса, Ecosystem, SDG 14 - Life Below Water, 1172 Environmental sciences, 0105 earth and related environmental sciences, INTERIOR ALASKA, coastal erosion, Hydrology, VULNERABILITY, NITROGEN DEPOSITION, Renewable Energy, Sustainability and the Environment, coastal erosion Supplementary material for this article is available, Public Health, Environmental and Occupational Health, Geovetenskap och miljövetenskap, 15. Life on land, dissolved organic carbon, Tundra, 13. Climate action, Soil water, Environmental science, [SDE.BE]Environmental Sciences/Biodiversity and Ecology, Environmental Sciences
Abstract

CT3 ; EnjS4; International audience; As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release will be offset by increased production of Arctic and boreal biomass; however, the lack of robust estimates of net carbon balance increases the risk of further overshooting international emissions targets. Precise empirical or model-based assessments of the critical factors driving carbon balance are unlikely in the near future, so to address this gap, we present estimates from 98 permafrost-region experts of the response of biomass, wild␣re, and hydrologic carbon ␣ux to climate change. Results suggest that contrary to model projections, total permafrost-region biomass could decrease due to water stress and disturbance, factors that are not adequately incorporated in current models. Assessments indicate that end-of-the-century organic carbon release from Arctic rivers and collapsing coastlines could increase by 75% while carbon loss via burning could increase four-fold. Experts identi␣ed water balance, shifts in vegetation community, and permafrost degradation as the key sources of uncertainty in predicting future system response. In combination with previous ␣ndings, results suggest the permafrost region will become a carbon source to the atmosphere by 2100 regardless of warming scenario but that 65%–85% of permafrost carbon release can still be avoided if human emissions are actively reduced.

Published
2016
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8. Reviews and syntheses : Effects of permafrost thaw on Arctic aquatic ecosystems

Author

Vonk, J. E., Tank, S. E., Bowden, W. B., Laurion, I., Vincent, W. F., Alekseychik, P., Amyot, M., Billet, M. F., Canário, J., Cory, R. M., Deshpande, B. N., Helbig, M., Jammet, M., Karlsson, J., Larouche, J., Macmillan, G., Rautio, M., Walter Anthony, K. M., Wickland, K. P., Organic geochemistry, NWO-VENI: Ancient organic matter that matters: The fate of Siberian Yedoma deposits, Organic geochemistry, and NWO-VENI: Ancient organic matter that matters: The fate of Siberian Yedoma deposits

Subjects
0106 biological sciences, 010504 meteorology & atmospheric sciences, Evolution, Earth science, lcsh:Life, 010501 environmental sciences, Permafrost, Freshwater ecosystem, 01 natural sciences, Thermokarst, Behavior and Systematics, lcsh:QH540-549.5, SDG 13 - Climate Action, Organic matter, 14. Life underwater, Thaw depth, Ecology, Evolution, Behavior and Systematics, Earth-Surface Processes, 0105 earth and related environmental sciences, chemistry.chemical_classification, Ekologi, geography, geography.geographical_feature_category, Ecology, Aquatic ecosystem, 010604 marine biology & hydrobiology, lcsh:QE1-996.5, Lake ecosystem, 15. Life on land, lcsh:Geology, lcsh:QH501-531, chemistry, Arctic, 13. Climate action, Environmental science, lcsh:Ecology
Abstract

The Arctic is a water-rich region, with freshwater systems covering 16 % of the northern permafrost landscape. The thawing of this permafrost creates new freshwater ecosystems, while at the same time modifying the existing lakes, streams, and rivers that are impacted by thaw. Here, we describe the current state of knowledge regarding how permafrost thaw affects lentic and lotic systems, exploring the effects of both thermokarst (thawing and collapse of ice-rich permafrost) and deepening of the active layer (the surface soil layer that thaws and refreezes each year). Within thermokarst, we further differentiate between the effects of thermokarst in lowland areas, vs. that on hillslopes. For almost all of the processes that we explore, the effects of thaw vary regionally, and between lake and stream systems. Much of this regional variation is caused by differences in ground ice content, topography, soil type, and permafrost coverage. Together, these modifying variables determine the degree to which permafrost thaw manifests as thermokarst, whether thermokarst leads to slumping or the formation of thermokarst lakes, and the manner in which constituent delivery to freshwater systems is altered by thaw. Differences in thaw-enabled constituent delivery can be considerable, with these modifying variables determining, for example, the balance between delivery of particulate vs. dissolved constituents, and inorganic vs. organic materials. Changes in the composition of thaw-impacted waters, coupled with changes in lake morphology, can strongly affect the physical and optical properties of thermokarst lakes. The ecology of thaw-impacted systems is also likely to change, with thaw-impacted lakes and streams having unique microbiological communities, and showing differences in respiration, primary production, and food web structure that are largely driven by differences in sediment, dissolved organic matter and nutrient delivery. The degree to which thaw enables the delivery of dissolved vs. particulate organic matter, coupled with the composition of that organic matter and the morphology and stratification characteristics of recipient systems will play an important role in determining the balance between the release of organic matter as greenhouse gases (CO2 and CH4), its burial in sediments, and its loss downstream. The magnitude of thaw impacts on northern aquatic ecosystems is increasing, as is the prevalence of thaw-impacted lakes and streams. There is therefore an urgent need to address the key gaps in understanding in order to predict the full effects of permafrost thaw on aquatic ecosystems throughout the Arctic, and their consequential feedbacks to climate.

Published
2015
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9. Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysis

Author

Vonk, J. E., Tank, S. E., Mann, P. J., Spencer, R. G M, Treat, C. C., Striegl, R. G., Abbott, B. W., Wickland, K. P., Organic geochemistry, NWO-VENI: Ancient organic matter that matters: The fate of Siberian Yedoma deposits, Department of Earth Sciences [Utrecht], Utrecht University [Utrecht], Arctic Center, University of Groningen [Groningen], Department of Biological Sciences, University of Alberta, Department of Geography, University of Northumbria at Newcastle [United Kingdom], Ecosystèmes, biodiversité, évolution [Rennes] (ECOBIO), Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Organic geochemistry, NWO-VENI: Ancient organic matter that matters: The fate of Siberian Yedoma deposits, Groningen Institute of Archaeology, Earth and Climate, Université de Rennes (UR)-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), and Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS)

Subjects
010504 meteorology & atmospheric sciences, Evolution, [SDV]Life Sciences [q-bio], Yedoma, lcsh:Life, F800, 010501 environmental sciences, Permafrost, 01 natural sciences, Behavior and Systematics, lcsh:QH540-549.5, Dissolved organic carbon, SDG 13 - Climate Action, Ecology, Evolution, Behavior and Systematics, 0105 earth and related environmental sciences, Earth-Surface Processes, 2. Zero hunger, Hydrology, Total organic carbon, Ecology, Aquatic ecosystem, lcsh:QE1-996.5, 15. Life on land, lcsh:Geology, lcsh:QH501-531, 13. Climate action, Soil water, Environmental science, Permafrost carbon cycle, lcsh:Ecology, Surface water
Abstract

As Arctic regions warm and frozen soils thaw, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to decomposition or transport. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the degradability of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of the mechanistic controls on DOC biodegradability is currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences commonly used in the literature. We also synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher DOC losses in both soil and aquatic systems. We hypothesize that the unique composition of (yedoma) permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively short flow path lengths and transport times, contributed to a higher overall terrestrial and freshwater DOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January–December) decrease in BDOC in large streams and rivers, but saw no apparent change in smaller streams or soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the thaw season progresses. Our results suggest that future climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC, the amount of BDOC, as well as its variability throughout the Arctic summer. We lastly recommend a standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Published
2015
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10. Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

Author

Organic geochemistry, NWO-VENI: Ancient organic matter that matters: The fate of Siberian Yedoma deposits, Vonk, J. E., Tank, S. E., Bowden, W. B., Laurion, I., Vincent, W. F., Alekseychik, P., Amyot, M., Billet, M. F., Canário, J., Cory, R. M., Deshpande, B. N., Helbig, M., Jammet, M., Karlsson, J., Larouche, J., Macmillan, G., Rautio, M., Walter Anthony, K. M., Wickland, K. P., Organic geochemistry, NWO-VENI: Ancient organic matter that matters: The fate of Siberian Yedoma deposits, Vonk, J. E., Tank, S. E., Bowden, W. B., Laurion, I., Vincent, W. F., Alekseychik, P., Amyot, M., Billet, M. F., Canário, J., Cory, R. M., Deshpande, B. N., Helbig, M., Jammet, M., Karlsson, J., Larouche, J., Macmillan, G., Rautio, M., Walter Anthony, K. M., and Wickland, K. P.

Published
2015

11. Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: A meta-analysis

Author

Organic geochemistry, NWO-VENI: Ancient organic matter that matters: The fate of Siberian Yedoma deposits, Vonk, J. E., Tank, S. E., Mann, P. J., Spencer, R. G M, Treat, C. C., Striegl, R. G., Abbott, B. W., Wickland, K. P., Organic geochemistry, NWO-VENI: Ancient organic matter that matters: The fate of Siberian Yedoma deposits, Vonk, J. E., Tank, S. E., Mann, P. J., Spencer, R. G M, Treat, C. C., Striegl, R. G., Abbott, B. W., and Wickland, K. P.

Published
2015

12. Reviews and Syntheses: Effects of permafrost thaw on arctic aquatic ecosystems

Author

Vonk, J. E., primary, Tank, S. E., additional, Bowden, W. B., additional, Laurion, I., additional, Vincent, W. F., additional, Alekseychik, P., additional, Amyot, M., additional, Billet, M. F., additional, Canário, J., additional, Cory, R. M., additional, Deshpande, B. N., additional, Helbig, M., additional, Jammet, M., additional, Karlsson, J., additional, Larouche, J., additional, MacMillan, G., additional, Rautio, M., additional, Walter Anthony, K. M., additional, and Wickland, K. P., additional

Published
2015
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20. Biodegradability of dissolved organic carbon in permafrost soils and waterways: a meta-analysis.

Author

Vonk, J. E., Tank, S. E., Mann, P. J., Spencer, R. G. M., Treat, C. C., Striegl, R. G., Abbott, B. W., and Wickland, K. P.

Subjects
SOIL moisture, WATERWAYS, BIODEGRADATION, CLIMATE change, BIODEGRADABLE materials
Abstract

As Arctic regions warm, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to thaw and decomposition. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the reactivity and subsequent fate of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism and its biodegradability will determine the extent and rate of carbon release from aquatic ecosystems to the atmosphere. Knowledge of the mechanistic controls on DOC biodegradability is however currently poor due to a scarcity of long-term data sets, limited spatial coverage of available data, and methodological diversity. Here, we performed parallel biodegradable DOC (BDOC) experiments at six Arctic sites (16 experiments) using a standardized incubation protocol to examine the effect of methodological differences used as common practice in the literature. We further synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-Arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher BDOC losses in both soil and aquatic systems. We hypothesize that the unique composition of permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively shorter flow path lengths and transport times, resulted in higher overall terrestrial and freshwater BDOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January-December) decrease in BDOC losses in large streams and rivers, but no apparent change in smaller streams and soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the seasons progress. Our results suggest that future, climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC as well as its variability throughout the Arctic summer. We lastly present a recommended standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic. [ABSTRACT FROM AUTHOR]

Published
2015
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25. The implications of microbial and substrate limitation for the fates of carbon in different organic soil horizon types: a mechanistically based model analysis.

Author

Y. He, Q. Zhuang, Harden, J. W., McGuire, A. D., Z. Fan, Y. Liu, and Wickland, K. P.

Subjects
BIOCHEMICAL substrates, SOIL moisture, SOIL microbiology, HISTOSOLS, SOIL horizons
Abstract

The large magnitudes of soil carbon stocks provide potentially large feedbacks to climate changes, highlighting the need to better understand and represent the environmental sensitivity of soil carbon decomposition. Most soil carbon decomposition models rely on empirical relationships omitting key biogeochemical mechanisms and their response to climate change is highly uncertain. In this study, we developed a multi-layer mechanistically based soil decomposition model framework for boreal forest ecosystems. A global sensitivity analysis was conducted to identify dominating biogeochemical processes and to highlight structural limitations. Our results indicate that substrate availability (limited by soil water diffusion and substrate quality) is likely to be a major constraint on soil decomposition in the fibrous horizon (40-60% of SOC pool size variation), while energy limited microbial activity in the amorphous horizon exerts a predominant control on soil decomposition (>70% of SOC pool size variation). Elevated temperature alleviated the energy constraint of microbial activity most notably in amorphous soils; whereas moisture only exhibited a marginal effect on dissolved substrate supply and microbial activity. Our study highlights the different decomposition properties and underlying mechanisms of soil dynamics between fibrous and amorphous soil horizons. Soil decomposition models should consider explicitly representing different boreal soil horizons and soil-microbial interactions to better characterize biogeochemical processes in boreal ecosystems. A more comprehensive representation of critical biogeochemical mechanisms of soil moisture effects may be required to improve the performance of the soil model we analyzed in this study. [ABSTRACT FROM AUTHOR]

Published
2014
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26. Lagged Wetland CH4Flux Response in a Historically Wet Year

Author

Turner, J., Desai, A. R., Thom, J., and Wickland, K. P.

Abstract

While a stimulating effect of plant primary productivity on soil carbon dioxide (CO2) emissions has been well documented, links between gross primary productivity (GPP) and wetland methane (CH4) emissions are less well investigated. Determination of the influence of primary productivity on wetland CH4emissions (FCH4) is complicated by confounding influences of water table level and temperature on CH4production, which also vary seasonally. Here, we evaluate the link between preceding GPP and subsequent FCH4at two fens in Wisconsin using eddy covariance flux towers, Lost Creek (US‐Los) and Allequash Creek (US‐ALQ). Both wetlands are mosaics of forested and shrub wetlands, with US‐Los being larger in scale and having a more open canopy. Co‐located sites with multi‐year observations of flux, hydrology, and meteorology provide an opportunity to measure and compare lag effects on FCH4without interference due to differing climate. Daily average FCH4from US‐Los reached a maximum of 47.7 ηmol CH4m−2s−1during the study period, while US‐ALQ was more than double at 117.9 ηmol CH4m−2s−1. The lagged influence of GPP on temperature‐normalized FCH4(Tair‐FCH4) was weaker and more delayed in a year with anomalously high precipitation than a following drier year at both sites. FCH4at US‐ALQ was lower coincident with higher stream discharge in the wet year (2019), potentially due to soil gas flushing during high precipitation events and lower water temperatures. Better understanding of the lagged influence of GPP on FCH4due to this study has implications for climate modeling and more accurate carbon budgeting. Research on what controls wetland methane emissions is continually advancing, and while this is beneficial for predicting future climate scenarios, there is still a need to understand how changes in plant productivity will influence wetland methane emissions. In this study, we investigated the strength and lag time of the relationship between gross primary productivity due to photosynthesizing plants and wetland methane flux in two closely situated sites. We also looked at how hydrology might change that relationship. We found the total amount of methane emitted in an extremely wet year was less than what was emitted in the following drier year at both wetlands potentially because of less carbon provided to the soil by photosynthesizing plants. The difference in methane emissions from one year to the next could be influenced by wetland hydrology, water temperature, or other conditions that impact methane‐producing bacteria. Results from this study will help scientists better predict methane emissions following high precipitation years which may become more common in a changing climate. Analyzed lagged response of methane flux to different driver variables at two closely located fen wetlands in WisconsinAir‐temperature normalization of methane flux was crucial for interpretation of lagged responses, especially in wet yearLagged response of methane flux to gross primary productivity surpassed 60 days and had weaker correlation during wet year at both sites Analyzed lagged response of methane flux to different driver variables at two closely located fen wetlands in Wisconsin Air‐temperature normalization of methane flux was crucial for interpretation of lagged responses, especially in wet year Lagged response of methane flux to gross primary productivity surpassed 60 days and had weaker correlation during wet year at both sites

Published
2021
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